I had a US citizen colleague who moved from Singapore to the UK and just got absolutely killed on tax - I can't remember the exact details but there was some ki

I had a US citizen colleague who moved from Singapore to the UK and just got absolutely killed on tax - I can't remember the exact details but there was some kind of annual (or less frequent) election he had to make that was correct for Singapore but meant he ended up paying full US and UK taxes on his income with very little relief.